1. Field of the Invention
The present invention relates to a ruthenium complex and, more particularly, a ruthenium complex suitable for Dye-Sensitized Solar Cell (DSSC).
2. Description of the Related Art
With the development of civilization, human beings in the whole world face serious problems of energy crisis and environmental pollution. One of the methods to solve these problems is to convert the solar energy into electrical energy directly by a photovoltaic solar cell. Among those solar cells, Dye-Sensitized Solar Cell is a prospective novel solar cell due to its good properties, such as low manufacturing costs, possibility of manufacture as a solar cell with large area, flexibility, light transmittance and possibility of using in the buildings.
In recent years, Grätzel et al. published a serial of articles relating to Dye-Sensitized Solar Cell (for example, O'Regan, B.; Grätzel, M. Nature 1991, 353, 737), which reveal that Dye-Sensitized Solar Cell can be applied practically. Generally, the structure of the Dye-Sensitized Solar Cell comprises a cathode, an anode, nano TiO2, dye and eletrolyte. The dye in the Dye-Sensitized Solar Cell has crucial affection to the efficiency of the cell. Thus, the ideal dye has to possess properties of ability of absorbing solar spectrum in a larger range, high absorption coefficient, high-temperature stability and light stability.
Grätzel's laboratory discovered a serial of ruthenium complex used to be the dye in the Dye-Sensitized Solar Cell. In 1993, Grätzel's laboratory disclosed a Dye-Sensitized Solar Cell prepared by N3 dye, of which the efficiency was up to 10.0% (AM 1.5). The incident photon to current conversion efficiency (IPCE) of the N3 dye could reach 80% in the range of 400 nm-600 nm. Thereafter, hundreds of dyes were discovered, but none of them could have the same efficiency of N3 dye. The structure of the N3 dye is shown in the following formula (a):

Until 2003, Grätzel's laboratory disclosed a Dye-Sensitized Solar Cell prepared by N719 dye, of which the efficiency was promoted to 10.85% (AM 1.5). The structure of N719 dye is the following formula (b):

In 2004, Grätzel's laboratory disclosed a Dye-Sensitized Solar Cell prepared by Black dye, of which the efficiency was 11.04% (AM 1.5). The Black dye can strengthen the spectrum response of red light area and infrared light area so that the efficiency of the dye-sensitized cell is improved. The structure of the Black dye is shown as the following formula (c):

Except for the ruthenium complex of N3 dye, N719 dye and Black dye disclosed by Grätzel's laboratory, there are several similar complexes, such as platinum complex, osmium complex, iron complex, copper complex, and so on. However, numerous researches show that the efficiency of the ruthenium complex is better.
The dye in the Dye-Sensitized Solar Cell has crucial affection to the efficiency of the cell. Therefore, one of the methods to improve the efficiency of the Dye-Sensitized Solar Cell is to find a dye molecule that could improve the efficiency of the Dye-Sensitized Solar Cell.